Magnetic core of an electromagnetic device having slots accommodating compacted electrical coil turns



y 5, 1969 J. E. LARSEN 3,456,142

MAGNETIC CORE OF AN ELECTROMAGNETIC DEVICE HAVING SLOTS ACGOMMODATING COMPACTED ELECTRICAL COIL TURNS Original Filed July 28, 1966 5 Sheets-Sheet 1 nvzeav sol/9C5 INVENTOR.

\ Jahnizar'san,

flttorney- July 15, 1969 J. E. LARSEN 3,456,142

MAGNETIC CORE OF AN ELECTROMAGNETIC DEVICE HAVING SLOTS ACCOMMODATING COMPACTED ELECTRICAL COIL TURNS I5 Sheets-Sheet 2 Original Filed July 28, 1966 INVENTOR. John A". Lartscfl;

27. C flfforny' July 15, 1969 J. E. LARSEN 3,456,142

MAGNETIC CORE OF AN ELECTROMAGNETIC DEVICE HAVING SLOTS ACCOMMODATING COMPACTEI) ELECTRICAL COIL TURNS Original Filed July 28, 1966 5 Sheets-Sheet 5 -62 74 i g 58 N 5 56 IN VENTOR. Jo/zn izans'am United States Patent 3,456,142 MAGNETIC CORE OF AN ELECTROMAGNETIC DEVICE HAVING SLOTS AC'COMMODATING COMPACTED ELECTRICAL COIL TURNS John E. Larsen, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Original application July 28, 1966, Ser. No. 568,588, now Patent No. 3,432,907, dated Mar. 18, 1969. Divided and this application July 5, 1968, Ser. No. 742,946 Int. Cl. H02k 3/12 US. Cl. 310-180 6 Claims ABSTRACT OF THE DISCLOSURE Electromagnetic devices carry conductive turns of electrical coils in the slots of magnetic cores. In at least one of these slots, a majority of these turns are compacted into non-circular cross-section configurations, the majority of the turns having relative positions and non-circular configurations primarily determined by forces acting thereon in the slot created by at least one electrical energy surge generated in the turns of sufficient magnitude to effect the desired construction. These forces acting on the turns are in the order of 10,000 pounds per square inch or more, with the turns as disposed in the slot having a slot space factor in excess of 60%, and preferably 80% and above. The magnetic cores not only incorporate unusually high slot space factors, but in addition, the turns are wedged tightly within the slot such that the tendency of turn movement relative to the magnetic core is effectively resisted.

Cross-reference to related application This application is a division of my co-pending application, Ser. No. 568,588, filed July 28, 1966 (now US. Patent 3,432,907 issued Mar. 18 1969), which in turn in part discloses subject matter disclosed in my still earlier filed application Ser. No. 414,822, filed Nov. 30, 1964 (now U.S. Patent 3,333,327 issued Aug. 1, 1967).

Background of the invention This invention relates generally to improved electromagnetic devices having electrically conductive turns formed with altered cross-section configurations. More particularly, the invention relates to improved electromagnetic devices having electrical coil turns of noncircular in cross-sectional areas and slots with high slot space factors.

Electromagnetic devices such as magnetic cores used in electrical motors, generators and the like customarily incorporate one or more electrical coils Wound from a number of relatively flexible insulated conductor turns. The manufacture and final construction of these devices has in the past posed certain problems, especially in the development of wound coils in the magnetic cores.

One of the manufacturing techniques used to place electrical conductor turns in the slots of magnetic cores during the development of Wound coils is that of winding conductor turns directly into the slots and thereafter compacting or pressing back the turns toward the slot bottoms. Another technique commonly used to place electrical conductor turns in core slots is that of forming a wound coil of conductor turns at one location and then transferring the wound coil into the core slots. However, in either technique, it is exceedingly difiicult to achieve slot space factors above 60%. Accordingly, the number of turns which can be placed in any one slot is limited when using these techniques. Even with conventional mechanical press-back equipment currently available, it is unusually diflicult to increase the slot space ice factors above when using conventional round or nearly round conductors, without appreciable problems, such as causing undue damage to the conductor insulation.

It is, therefore, desirable to be able to achieve higher slot space factors (in excess of 60% and preferably the above) than were heretofore feasible, while avoiding the well-known difficulties involved with the use of conventional mechanical press-back equipment (e.g., expense, lack of speed, and damage to wire insulation). This is especially desirable as it will allow more conductor turns to be placed in any one slot and will therefore allow relatively inexpensive aluminum conductor wire to be more widely used as compared with copper wire for a given core design. More turns of aluminum than copper conductors are required, of course, for a given slot volume to achieve the same rating in view of the differences in their electrical conductivity properties. Further, it is desirable to be able to wedge conductor turns into the slots of magnetic cores, regardless of the slot configuration, thereby to retain the turns in the slots without the need for auxiliary holding means during subsequent stages of fabrication.

In the pending United States patent applications Ser. No. 414,822, 414,823, 414,824, 414,825, 414,826, now Patents 3,333,327-3,333,330 inclusive and 3,333,335, all of which are assigned to the same assignee as this invention, novel and unique ways are disclosed for performing various coil transforming operations by utilizing electrical energy. It is highly desirable to make use of the electrical energy approach to accomplish the desired results set forth above.

Summary of the invention Accordingly, it is an object of the instant invention to provide an improved magnetic core for use in an electromagnetic device which achieves at least some of the desirable results mentioned above.

A more specific object of the present invention is the provision of an improved magnetic core useful in electromagnetic devices which has compacted coil turns in selected slots of the core primarily positioned therein by forces created by electrical energy and slot space factors in excess of 60%.

Another specific object of the instant invention is the provision of an improved yet inexpensive electromagnetic device magnetic core having turn positions in selected slots primarily determined by forces created by electrical energy, high slot sp'ace factors, and turns tightly wedged within the slots which tend to resist movement of the turn in the slots relative to the magnetic core.

The invention is carried out in one form in the illustrated embodiments in connection with a magnetic core of an eletcromagnetic device. At least one selected slot of the core carries turns of an electrical coil in which a majority of the conductors or turns are compacted, having non-circular cross-sectional configurations and position in the given slot to furnish a slot space factor in excess of 60%, and preferably 80% or more. The non-circular cross-sectional configurations and relative positions in the slot for the turn majority are primarily determined by forces acting thereon which are created by electrical energy surges generated in the turn majority of sufficient magnitude to effect the construction.

In cores having the above construction, the turn majority is tightly wedged within the slot carrying them such that there is a tendency of movement of the turn majority relative to the magnetic core to be resisted as a unit, regardless of slot configuration or contour. Moreover, in spite of the foregoing beneficial features derived with this structure, no undue damage has been caused to the conductors, and core fabrication is permitted with improved yet inexpensive processes and apparatus.

The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention itself, however, together with further objects and advantages thereof may be best understood by reference to the following description taken in conjunction with the accompanying drawings.

Brief description of the drawings FIGURE 1 is an end view of a stator core as the illustrated exempli-fication of my invention, with two coil groups shown in the coil accommodating slots of the core, and including first exemplified apparatus for carrying out one way of altering or developing the turns in selected coil accommodating slots of the core to produce the improved construction of the present invention;

FIGURE 2 is a fragmentary perspective view of the stator core and apparatus illustrated in FIGURE 1, showing schematically the connection of a rigid conductor means to a source of electrical energy, and with one wound coil illustrated in initial, intermediate and final altered or developed positions in the core;

FIGURE 3 is an enlarged fragmentary view of one coil accommodating slot of the stator shown in FIGURES '1 and 2, illustrating the distribution of the individual conductors after insertion of a coil side portion into the slot and prior to the altering or development of the conductor turns in the slot, with the rigid conductor means in a first position in the slot relative to the conductor turns and the electrically conductive non-magnetic material;

FIGURE 4 is an enlarged fragmentary view of the coil accommodating slot and apparatus illustrated in FIG- URE 3, the view of FIGURE 4 showing the compaction, change in cross-section of the conductor turns, relative positions of the turns in the slot, and also the view showing the rigid conductor means in its supported position;

FIGURE 5 is a perspective view, partially in cross-section, of another form of apparatus useful in providing the improved construction of the stator core in the exemplification;

FIGURE 6 is a vertical sectional view taken substantially on the plane of the line 66 of FIGURE 5;

FIGURE 7 is a vertical sectional view taken substantially on the plane of the line 7-7 of FIGURE 6;

FIGURE 8 is an enlarged fragmentary view of one coil accommodating slot illustrating the final distribution of the individual conductor turns carried therein when utilizing the apparatus illustrated in FIGURES S7; and

FIGURE 9 is a partial perspective view, partially in vertical section of one coil accommodatingslot of a stator, and still another exemplified form of apparatus useful in furnishing the desired core and core and coil construction.

Description of preferred embodiments For the purpose of explaining the principles of my invention, I have illustrated in FIGURES 1-4 inclusive various aspects of my improved invention in connection with a stator core, generally denoted by reference numeral 10. The core 10 carries two coil groups 12 and 14 comprising the main running winding for a two-pole induction motor. It will be noted that each coil group 12 and 14 includes five wound coils, each coil including a plurality of individually wound insulated flexible conductor turns. The exemplified stator core 10 includes twenty-four coil accommodating slots for accommodating the wound coils. In a stator core of the type illustrated in FIGURE 1, opposed coil accommodating slots such as 16, 18, and 22, 24, and 26, 28 each carry one wound coil therein. As will be noted, I have illustrated in cross section the individual conductor turns 21 of the one wound coil 20 carried in the stator core coil accommodating slots 16 and 18.

In the illustrated exemplification, the one wound coil 20 includes forty individual conductor turns 21, the side portions of the coil 20 being accommodated in the slots 16 and 18 and the end turn portions proejcting axially beyond the stator end faces 19. In addition, the three pairs of slots 16, 18; 22, 24; and 26, 28 each carry coils composed of a relatively large number of individual conductor turns. Further, the slot pairs 22, 24 and 26', 28 are adapted to receive start windings including additional conductor turns as well as the conductor turns of the wound coils comprising a portion of the main or running winding. Accordingly, it is most desirable to press back the coil side portions of the coils carried in these three pairs of slots in order to accommodate the maximum number of turns. As explained above, it is desirable to achieve the highest possible slot space factor, or the greatest ratio of slot area actually filled with conductor turns as compared to the available slot area so as to accommodate the maximum number of turns therein, While not damaging the conductor insulation. In FIGURE 3, I have illustrated the forty conductor turns 21 of the wound coil 20 located in the slot 18 after the side portions of the wound coil have been inserted in the slot and prior to the altering or developing method of my invention. As will be noted in FIGURE 3, the conductor turns 21 are loosely located in the slot 18, with voids or spaces therebetween, and hence the slot space factor is relatively low. It is anticipated, for example, that if the Wound coil 20 were placed in the stator core 10 by a machine, such as is disclosed in the US. Patent 2,934,099 granted to Lowell M. Mason on Apr. 26, 1960, the slot space factor would be in the neighborhood of 60%.

To compact the individual conductors in the slot 18 in order to achieve a slot space factor in excess of 60%, preferably in the range of to I support rigid conductor means generally denoted by reference numeral 22 in the slot 18 between the slot entrance 25 and the slot bottom wall 31. The rigid conductor means 22 is thereby in inductively or transformer-coupled relationship with the conductor turns 21 located in the slot 18. The coil 20 provides a closed path for the flow of induced current. In the exemplification, I connect the rigid conductor means 22 across the output terminals 27 and 29 of an energy surge source generally denoted by reference numeral 32.

The energy surge source 32 used in the illustrative exemplification of the invention may be any suitable source, such as one of the capacitor discharge energy sources disclosed in my aforementioned U.S. Patent 3,333,327. In the present exemplification, it should be capable of supplying a high power electrical surge or pulse of at least 5,000 joules at 3000 volts across the output terminals 27 and 29. Accordingly, when the surge source 32 is activated, an energy surge of preselected intensity is injected into the rigid conductor means 22 thereby establishing a transient magnetic field about the rigid conductor means, and inducing current flow in the Wound coil 20. It is believed that the instantaneous current flow through the wound coil 20 establishes a transient magnetic field thereabout which interacts with the field about the rigid conductor means 22, creating electromagnetic forces which force the conductor turns 21 toward the bottom 31 of the slot 18.

The finally developed or altered configuration of the turns is illustrated in FIGURE 4. It will be understood that if the electrical pulse or surge of energy injected into the rigid conductor means 22 is of great enough magnitude, it will force the conductor turns of the coil 20 against the slot bottom 31 with sufficient force to change the crosssection of at least the majority of the conductor turns carried in the slot. This final conductor configuration will be seen in FIGURE 4. Further, after the core is saturated, it is believed that additional compaction of the coil is achieved by attractive forces between the individual coil turns. It is also believed that such core saturation occurs almost instantaneously, or during the initial portion of the energy surge. Typically, it has been estimated or determined that in order to change the cross-section of a majority of initially round aluminum conductors in the given slot to a non-circular configuration, approximately 10,000 pounds per square inch must be applied against the conductors, and to achieve somewhat similar results with copper conductors having initially round cross-section areas, approximately 18,000 pounds per square inch must be applied thereagainst.

The forces generated against the conductor turns in the stator slots by the exemplification is of suflicient magnitude to change the cross-section area or configuration of at least a majority of the conductors in the slot and hence achieve an unusually high slot space factor, well over 60%. Stated otherwise, the voids or spaces between the conductor turns in the slot are virtually eliminated by the resulting surface-to-surface contact between the previously round conductors as the conductors change crosssection in response to the force thereagainst. Further, the change of cross-section is attained without deleteriously affecting the quality of the insulation covering the wire. It should also be understood that there is a wedging effect produced by this change of cross-section of the conductors wherein the conductors are wedged in the slot. The conductor turns will therefore be retained in the slot without the need for auxiliary holding means to retain them in the slot as the stator core is transferred during subsequent stages of fabrication.

In applying my invention to a two-pole stator core similar to the one illustrated in FIGURES 1 and 2, and particularly to a wound coil comprised of forty conductor turns and wound to an original slot space factor of 63% carried in such a stator core, an energy surge of 2,767.5 joules at 3000 volts was injected into the rigid conductor means 22 supported in the coil accommodating slot 18. The resulting current flow through the rigid conductor means was approximately 75,000 amperes (peak) and the final slot space factor, 'as illustrated in FIGURE 4 was calculated to be approximately 90%. The conductor turns in this instance were 0.0508 inch diameter aluminum wire insulated with polyvinyl formal or Formex insulation, and the rigid conductor means 22 illustrated in FIGURE 3 was 0.096 by 0.160 inch rectangular insulated copper.

In connection with another stator core 10, rigid conductor means similar to means 22 was used to compact and alter the configuration of 51 conductor turns carried in a stator slot. The conductor turns in this instance were 0.0427 inch diameter copper wire insulated with Formex insulation, and the energy injected into the conductor means 22 was approximately 4,590 joules at 3000 volts. The resulting current flow in the rigid conductor means was 9,000 amperes (maximum) and the resulting compaction and alteration of the conductor turns carried in the slot was similar to the results illustrated in FIG- URE 4, a slot space factor of approximately 90% being attained.

Referring again to FIGURES 1-4 inclusive in order to explain how the method described above was carried out in actual practice, to form a magnetic core constructed in accordance with one form of my invention, I will now more fully describe the rigid conductor means 22 and the manner in which it was supported in the stator slots. The rigid conductor means 22, as illustrated in FIGURE 2, comprises a generally U-shaped member 23 of electrically conductive material, the material actually used being copper in this instance. The member 23 includes two opposed leg portions 28 and 30 connected by a bight portion 33. The leg and bight portions are generally rectangular in cross-section (in one exemplification 0.096 by 0.160 inch). The opposed leg portions 28 and 30 of the member 23 are shaped to fit into the core slots, and are moved into opposed coil accommodating slots 26 and 28 axially from one end of the stator. These slots 26 and 28 accommodate the side portions 36 of the wound coil 20 therein. At each free end of the leg portions 28 and 30 there are suitable terminals 34 to enable the structure 23 to be connected across the output terminals 27 and 29 of an electrical energy surge source 32 as illustrated in FIGURE 2.

Referring further to FIGURE 2, it will be observed that the wound coil 20 is illustrated schematically in full lines in its final location relative to the core 10, with the coil side portions 36 pressed toward the slot bottoms 31 of the coil accommodating slots 26 and 28 and with the end turn portions 38 pressed back towards the stator core end faces 19. I have also shown the initial location of the wound coil 20 in the slots 26 and 28 at 42, and an intermediate location at 44. The three locations of the coil 20 in the slots 26 and 28 are shown in this manner in order to illustrate further details of the Way in which the improved core construction was attained.

The initial designation 42 denotes the location of the coil when it is placed in the slots by a suitable machine for that purpose. The intermediate designation 44 denotes the coil location after an initial energy surge is injected into the structure 23. When the initial energy surge of energy is injected into the member 23 from surge source 32, the coil 20 is moved to the intermediate position 44 with the coil side portions 36 adjacent the slot bottoms; however, the coil end turn portions 38 are only slightly affected. The wound coil 20 is then connected across the output terminals 27, 29 of the surge source 32 and the terminals 34 of the member 23 are shorted together to provide a closed electrical path in the member. With a rigid structure 46 of electrically conductive non-magnetic material capable of conducting eddy currents disposed in the stator bore 48, a surge of energy is then injected directly into the wound coil 20. Electromagnetic forces are created between the coil end turn portions 38 and the structure 46 and the coil end turn portions 38 are moved to their final location adjacent the stator end faces 19, as shown in FIGURE 2. The side portions 36 of the coil 20 will also be further compacted at this time.

As will be seen in FIGURES 1 and 2, the structure 46 comprises a generally cylindrical member shaped to fit the stator bore 48 and includes an insulative layer 50 for the electrically insulating the structure 46 from the conductor windings. The insulative layer may either be a separate hollow member or integrally formed on the surface of the structure 46, as desired. Since the structure 46 is capable of conducting eddy currents, when current flows in the wound coil 20, an interaction of electromagnetic forces takes place between the coil end turn portions 38 and the structure 46 to press the end turn portions to the position illustrated in FIGURE 2.

It will be understood that the U-shaped member 23 may be mechanically supported in the stator core 10 by suitable supporting means, if so desired. I have found, however, that the structure 46 comprises means for supporting member 23 in the coil accommodating slots 26 and 28. The support is achieved by electromagnetic forces established between the member 23 and the conductor turns 21 in the slots 26 and 28 and the structure 46 when an energy surge is injected into either the member 23 or the coil 20. Thus, it is believed that equal and opposing forces are established between the member 23 and the conductor turns 21 and between the member 23 and the structure 46, the forces acting to rigidly support the member 23 somewhere between the turns 21 and the structure 46. Since the forces are opposing, and only the turns and the member 23 are movable, the forces will balance or equalize when the turns have been pressed toward the slot bottom 31 as far as possible and when the member 23 is at a predetermined location between the conductor turns 21 and the structure 46, as illustrated in FIGURE 4. Of course, it will be understood that the force generated between the member 23 and the conductor turns 21 of the coil 20 forces the conductor turns downwardly towards the slot bottom 31 as well as balancing the opposing force generated between the member 23 and the structure 46.

While I have described one way in which the desired core and coil construction can be attained by the exemplitied apparatus of FIGURES 1-4, similar results may also be obtained with the apparatus illustrated in FIGURES 5-8 inclusive where I have shown a second type of rigid conductor means. Referring first to FIGURE 5, wherein like numerals refer to like parts, the second form of rigid conductor means is generally denoted by reference numeral 52 and includes a rigid conductor carrying structure or fixture 54 shaped to fit the bore of a stator such as the stator 10. The structure 54 is a generally cylindrical, elongate member constructed of electrically conductive non-magnetic material 56 capable of conducting eddy currents and has portions encapsulated by suitable insulating material 58. The structure 54 carries three pairs of rigid conductor bars, the pairs being generally denoted by the reference numerals 60, 62, 64, respectively. Each pair of conductor bars comprises a generally U-shaped member which includes leg portions 66 and 68 and an interconnecting bight portion 70, as will be observed, for example, in FIGURE 6. The leg portions 66 and 68 extend radially outwardly of and axially along the carrying structure 54, being mounted in insulated slots 72 which extend axially along the structure as will be seen in FIGURE 8, for example. Further, each leg portion of the three pairs of conductor bars includes an upstanding portion 74 of generally oblong cross-section, shaped to fit axially into a stator core coil accommodating slot such as the slot 76 illustrated in FIGURE 8. Each upstanding portion 74 is insulated as at 80, to insure against the possibility of its shorting with the conductor turns 82, carried in the slot 76.

Referring again to FIGURE 5, it will be seen that a shunt ring 84 is mounted in the structure 54 and retained by the encapsulating insulation 58. The shunt ring 84 is in contact with each pair of conductor bars, thereby to provide a parallel electrical conduction across the three pairs 60, 62 and 64 of the conductor bars. Inwardly disposed portions 86 and 88 of the shunt ring 84 have terminals 90 and 92 respectively extending axially therefrom. The terminals 90 and 92 are supported in a rounded end portion of the structure 54 generally denoted by reference numeral 94, and rigidly maintained by the insulation 58, with portions of the terminals extending outwardly of the end portion 94 to enable electrical connections to be made therewith. The rounded end portion 94 is provided to enable the structure 54 to be easily moved into the bore of the stator core 10, as it will push back the end turns which may block the bore.

The rigid conductor carrying structure or fixture 54 is mounted as by mounting screws 98 and 100 on a mounting block 102, thereby being situated to receive the stator core in coil altering position thereon. Thus, the stator core 10 may be moved axially onto the structure 54, with the pairs of conductor bars 60, 62, and 64 thereby being moved into opposed pairs of coil accommodating slots 76 carrying the side portions of wound coils therein. The conductor bars are supported in the stator slots 76, when the stator core 10 is in place, by the structure 54 which lies adjacent to the entrances of the slots.

In using the apparatus illustrated in FIGURES 5-8 inclusive, an energy surge is injected into the pairs of conductor bars through the terminals 90 and 92 and shunt ring 84. The three wound coils carried in the three pairs of slots in which the three pairs of conductor bars 60, 162, and 64 are supported, are connected to provide a closed path for the flow of induced current. Electromagnetic forces are thus created between the conductor bars and these wound coils thereby compacting the coil side portions toward the bottoms of these slots, as illustrated in FIGURE 8. It will be noted that the cross-section of the coil side portions is changed during the coil compaction thereby achieving a high space factor as contemplated by my method. Further, it will be understood that by using the apparatus of FIGURES 58, the configuration of three wound coils may be altered (i.e., the coils developed) at the same time. Thus, the three wound coils carried in the slot pairs in which it is most desirable to attain high space factors (i.e., the slot pairs which receive the greatest total number of conductor turns therein) may be compacted in one quick, efficient operation. Further, the end turn portions of the wound coils will normally be generally adjacent the electrically conductive nonmagnetic portion 56 of the structure 54 when the stator core is mounted on the structure 54, and hence the end turn portions of the coils will also be compacted and forced back toward the stator faces when using the apparatus of FIGURES 58.

Referring now to FIGURE 9, it will be observed that there is illustrated yet another exemplified apparatus for achieving the desired results. I have shown in FIGURE 9 another rigid conductor means, in this instance, generally denoted by reference numeral 106-. The means 106 comprises a plurality of flexible electrically conductive wires 108 rigidly mounted or contained in a rigid insulator structure 110. The insulator structure 110 is shaped to fit axially into a coil accommodating slot such as the slot 112 and may be constructed of a suitable thermosetting material such as thermosetting epoxy resin, which will normally be formed about the plurality of conductive wires 108 in order to rigidly support the wires 108 in insulated, spaced apart position. The structure 110- further includes a stiffening means in the form of a generally T-shaped member 116 suitably attached to the bottom of the structure. The stitfening means 116 is provided in order to insure that when forces are generated between the rigid conductor means 106 and the conductor turns carried in the slot 112, the conductor means 106 will remain rigid. While I have shown only one rigid conductor means 106 supported in one coil accommodating slot 112, it will be understood that any desired number of such means 106 may be supported in various of the slots of a stator core at one time. It would normally be the case, for example, that two such structures 110 would be supported in two opposed slots of a core carrying therein the two side portions of one wound coil by supporting means (not illustrated) at one end of the structures 110 adjacent the end face of the stator core.

In order to illustrate more fully how one form of the invention has been carried out in actual practice, the following example is given in connection with the stator and rigid conductor means in the general form of the apparatus illustrated in FIGURES 58 inclusive, already discussed. The structure 54 was disposed in a stator bore, with the three pairs of conductor bars 60, 62, and 64 being rigidly supported in three pairs of coil accommodating slots of a two-pole stator containing 0.0508 inch diameter conductor turns of aluminum conductor wire insulated with Formex insulation. Two surges of electrical energy at approximately 4,590 joules at 3000 volts were injected into the rigid conductor bars, with 115,000 amperes (maximum) flowing through the bars on the first pulse, and 107,000 amperes maximum) flowing through the bars on the second pulse. A third pulse was then injected into the bars at an energy level of approximately 5,655 joules at 3300 volts, producing 115,000 amperes (maximum) therein. The rigid conductor means or :bar pairs 60, 62, and 64 were then disconnected from the energy surge source, and three wound coils carried in the three pairs of coil accommodating slots serially connected together and connected across the energy surge source 32. With the three pairs of conductor bars 60-, 6-2 and 64 connected to provide a closed path for the flow of induced current, an energy surge of approximately 5,100 joules at 1000 volts was injected into the three wound coils. By the above steps, the side portions of the three serially connected wound coils were compacted in their stator slots, the cross-section of a majority of the conductor turns in these slots was changed, and a rela- 9 tively high space factor (approximately 79%, 73% and 70% for the outer, intermediate and inner coils respectively) Was achieved. Further, the end turn portions of the three wound coils were pressed back toward the stator end faces, and the three wound coils were thereby fully developed into a final desired configuration.

In view of the foregoing, it will be apparent that the present invention provides an improved, yet inexpensive magnetic core carrying electrical coils for use in electromagnetic devices having slot space factors in excess of 60% and even 80% and above. In addition, the construction is such that in at least one preselected slot, a majority of the conductor turns have non-circular crosssection areas and relative positions With respect to the magnetic core which tend to resist movement in the slots. The relative turn positions, attained in the slot primarily by forces created by electrical energy, are such that the turns will obviously experience less stress when the core is subsequently energized in actual operation. These and other beneficial features are obtained without adversely affecting conductor insulation and at the same time improved methods and apparatus may be employed in the fabrication of the electromagnetic device. Also, in some applications, it is possible by the present invention to substitute relatively less expensive insulated aluminum conductor wire for copper wire.

Although the principles of my invention have been illustrated quite advantageous in regard to stator constructions, it will be apparent to those skilled in the art that the principles of the invention may also be employed effectively in other electromagnetic devices having magnetic cores. It will thus be apparent that numerous changes and modifications may be made therein without departing from the invention. It is, therefore, intended in the appended claims to cover all such equivalent modifications and variations that fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electromagnetic device comprising a magnetic core having at least one preselected coil-accommodating slot and an electrical coil including compacted turns disposed in the at least one preselected coil-accommodating slot, a majority of said turns having non-circular crosssection configurations and the turns having relative positions in said at least one preselected slot primarily determined by forces acting on the turns in the slot created by an electrical energy surge generated in the turns of sufiicient magnitude to effect said configurations and relative turn positions.

2. The electromagnetic device of claim 1 in which the non-circular cross-section configurations of the majority of turns and relative turn positions for the compacted turns in the at least one coil-accommodating slot are determined by forces acting thereon of approximately 10,000 pounds per square inch or more.

3. The electromagnetic device of claim 1 in which the non-circular cross-section configurations of the turn majority and relative turn positions provide a slot space factor for the compacted turns in the at least one coilaccommodating slot of 80% or more, with the compacted turns being wedged tightly together in the at least one coil-accommodating slot thereby tending to resist movement relative to the magnetic core.

4. An electromagnetic device comprising a magnetic core having at least one coil-accommodating slot carrying compacted turns of an electrical coil, a majority of said turns being non-circular in cross-sectional configuration and positioned in the slot to form a slot space factor therein in excess of said non-circular cross-sectional configuration and slot space factor being primarily determined by an electrical energy surge generated in said turns of sufiicient magnitude to create electromagnetic forces acting on the turns carried in the at least one coilaccommodating slot.

5. The electromagnetic device of claim 4 in which the non-circular cross-section configurations of the majority of turns and relative turn positions for the compacted turns in the at least one coil-accommodating slot are primarily determined by forces acting thereon of approximately 10,000 pounds per square inch or more.

6. The electromagnetic device of claim 4 in which the non-circular cross-section configurations of the turn majority and relative turn positions provide a slot space factor for the compacted turns in the at least one coilaccommodating slot of or more, with the compacted turns being wedged tightly together in the at least one coil-accommodating slot thereby tending to resist movement as a unit relative to the magnetic core.

References Cited UNITED STATES PATENTS 2,506,173 5/1950 Polard 29-205 2,998,540 8/1961 Phillips 310214 3,333,327 8/1967 Larsen ,29-596 3,348,183 10/1967 Hodges et al. 336-223 3,353,251 11/1967 Linkous 29205 WARREN E. RAY, Primary Examiner US. Cl. X.R. 310- 

